Implement server side cluster resolving (#926)
* Implement server side cluster resolving
```
.......................
----------------------------------------------------------------------
Ran 23 tests in 0.428s
OK
Name Stmts Miss Cover Missing
--------------------------------------------------------------------------
/pytorch/xla/torch_xla_py/xla_dist.py 173 12 93% 12-13, 52, 82, 172, 175, 186-189, 239, 251, 283, 326
/pytorch/xla/torch_xla_py/xla_dist_test.py 257 4 98% 249, 267-268, 734
--------------------------------------------------------------------------
TOTAL 430 16 96%
```
